MISFET semiconductor device having a high dielectric constant insulating film with tapered end portions

ABSTRACT

There is provided a semiconductor device configured as follows. On a semiconductor substrate, a titanium oxide film which is an insulating film having a higher dielectric constant than that of a silicon dioxide film is formed as a gate insulating film, and a gate electrode is disposed thereon, resulting in a field effect transistor. The end portions in the gate length direction of the titanium oxide film are positioned inwardly from the respective end portions on the source side and on the drain side of the gate electrode, and the end portions of the titanium oxide film are positioned in a region in which the gate electrode overlaps with the source region and the drain region in plan configuration. This semiconductor device operates at a high speed, and is excellent in short channel characteristics and driving current. Further, in the semiconductor device, the amount of metallic elements introduced into a silicon substrate is small.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device, and amanufacturing method thereof. More particularly, it relates to asemiconductor device having a MISFET in which an insulating film havinga higher dielectric constant than that of a conventional silicon dioxidefilm is used as a gate insulating film, and a manufacturing methodthereof.

2. Description of the Related Art

The technical development in a semiconductor device has been pursuedfrom three viewpoints of an increase in integration, a reduction inelectric power consumption, and an increase in speed. Out of these, thereduction in electric power consumption and the increase in speed in theMISFET are the mutually contradictory challenges. For achieving thecompatibility therebetween, the reduction in thickness of a gateinsulating film exceeding the trend in the prior art has been required.On the other hand, a silicon dioxide film which has been used as a gateinsulating film in the prior art has advantages in that it is excellentin interface characteristics with a silicon substrate, and in that ithas a large band gap as an insulating film. However, it has a dielectricconstant of 3.8 to 3.9. Thus, the film thickness is required to be setat around 3 nm even for meeting the current requirements on the deviceperformances. The film thickness of the insulating film is determined bya necessary channel induced charge amount. The channel induced chargeamount Qc is expressed as the following equation:

Qc=V·∈ ₀ ·∈/t (q/cm ²)

where t denotes the gate insulating film thickness, ∈ denotes thedielectric constant, ∈₀ denotes the dielectric constant of vacuum, and Vdenotes the voltage applied to the gate insulating film. If theinsulating film is reduced in film thickness down to 3 nm or less, thereis observed a current (direct tunnel current) which flows by directlytunneling in the insulating film between a gate electrode and thesilicon substrate. This current is very large. For this reason, it isconsidered difficult to reduce the film thickness more than now with thesilicon dioxide film.

For avoiding this problem, the use of an insulating film having a largedielectric constant, ∈ is effective. The reason for this is that the Qcis proportional to ∈, and inversely proportional to the film thickness tas apparent from the equation shown above. As the insulating film havinga large dielectric constant ∈, there is known an oxide film of titanium,tantalum, hafnium, zirconium, aluminium, lanthanum, strontium, selenium,or the like. For example, in the paper issued to B. He et al., (1998International Electron Device Meeting Technical Digest, p.p. 1038-1040),there is described the characteristic of a MIS (metal insulator silicon)structure using a titanium oxide film. There is also described that evenan insulating film with a film thickness of 1.1 nm (EOT; EquivalentOxide Thickness) in terms of the dielectric constant of a silicondioxide film can also inhibit the direct tunnel current.

Further, in JP-A No. Hei 11-3990, there is described as follows. When ahigh dielectric constant material is used as a gate insulating film, anincrease in gate electric field increases the current leakage, andthereby deteriorates the element characteristics. Further, the overlapbetween the gate electric field and the drain electric field causes theshort channel effect. For avoiding the foregoing problems, there isdisclosed the following semiconductor device. In this semiconductordevice, a gate insulating film is formed with a shorter length in thegate length direction than that of a gate electrode. A space or adielectric having a lower dielectric constant than that of the gateinsulating film is provided laterally in the gate length direction ofthe gate insulating film, and in the region, which is sandwiched betweenthe gate electrode and a semiconductor substrate, and in which at leastthe gate electrode and a diffusion layer overlap on each other as seenfrom the top.

As described in the paper to B. He et al., when an insulating filmhaving a high dielectric constant such as a titanium oxide film is used,even if the EOT is reduced to 1 nm or less, the physical film thicknessof the insulating film is sufficiently large. Therefore, it is possibleto inhibit the direct tunnel current. However, this technology has givenno consideration to the following fact. Namely, the insulating filmhaving a high dielectric constant is a metal oxide of titanium,tantalum, or the like. Accordingly, incorporation of such a metal intothe silicon substrate causes an increase in junction leakage, and thelike. In a conventional MISFET formation process, in general, the gateinsulating film is left at the time of gate electrode processing, andsource and drain regions are formed with an ion implantation method byusing this film as a through film for ion implantation. However, ifmetallic elements are contained in the gate insulating film at thisstep, it is unavoidable that the metallic elements are introduced intothe silicon substrate due to the knock-on effect.

Further, the paper of (IEEE Transaction on Electron Devices, volume 46,Number 7, July 1999, PP. 1537 to 1544) to B. Cheng., et al., indicatesas follows. Namely, when a high dielectric constant insulating film isused as a gate insulating film, the device performances are reduced bythe fringe effect due to an increase in the capacitance (fringecapacitance) between the gate edge and the source/drain.

Still further, the foregoing prior art described in JP-A No. Hei 11-3990has given no consideration to the following fact. Namely, in the regionin which the gate electrode and the diffusion layer overlap on eachother as seen from the top, a space or a dielectric having a lowerdielectric constant than that of a gate insulating film is present.Further, no gate insulating film is disposed on top of the diffusionlayer. Therefore, it is difficult to achieve a higher speed.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a semiconductordevice in which an insulating film having a higher dielectric constantthan that of a silicon dioxide is used as a gate insulating film, andwhich operates at a high speed, and is excellent in short channelcharacteristics, and driving current, and in which the amount ofmetallic elements introduced into a silicon substrate is small.

A second object of the present invention is to provide a method formanufacturing a semiconductor device in which an insulating film havinga higher dielectric constant than that of a silicon dioxide is used as agate insulating film, and which operates at a high speed, and isexcellent in short channel characteristics, and driving current, and inwhich the amount of metallic elements introduced into a siliconsubstrate is small.

In order to attain the first object, a semiconductor device according toone aspect of the present invention has a field effect transistor whichincludes a semiconductor substrate, a gate insulating film on thesemiconductor substrate, and a gate electrode disposed via the gateinsulating film on the semiconductor substrate, wherein the gateinsulating film is an insulating film having a higher dielectricconstant than that of a silicon dioxide film, the end portions in thegate length direction of the gate insulating film are positionedinwardly from the respective end portions on the source side and on thedrain side of the gate electrode, and the end portions of the gateinsulating film are positioned in a region in which the gate electrodeoverlaps with a source region and a drain region in plan configuration.

Further, in order to attain the first object, a semiconductor deviceaccording to another aspect of the present invention has a field effecttransistor which includes a semiconductor substrate, a gate insulatingfilm on the semiconductor substrate, and a gate electrode disposed viathe gate insulating film on the semiconductor substrate, wherein thegate insulating film is an insulating film having a higher dielectricconstant than that of a silicon dioxide film, and the end portions inthe gate length direction thereof are positioned inwardly from therespective end portions on the source side and on the drain side of thegate electrode, and a source region and a drain region of the fieldeffect transistor extend into the underlying portion of the gateinsulating film.

In either of the semiconductor devices, the end portions of the gateinsulating film are respectively the end portions of the site which islargest in thickness. In other words, when the gate insulating film ismade of a plurality of layers, and the positions of respective endportions thereof differ from one another, the inside between theportions positioned most inwardly from the end portions of the gateelectrode corresponds to the thickest site of the gate insulating film.Accordingly, the portions are respectively the end portions of the gateinsulating film. Further, even when the end portions of the gateinsulating film are not perpendicular to the substrate, the portionspositioned most inwardly from the end portions of the gate electrode arerespectively the end portions thereof.

It is preferable that the end portions in the gate length direction ofthe gate insulating film are positioned inwardly from the respective endportions on the source side and on the drain side of the gate electrodeby 15 nm to 25 nm, respectively. It is preferable that as the gateinsulating film, the oxide, the oxynitride, the silicate compound, orthe like of at least one metal selected from the group consisting oftitanium, tantalum, hafnium, zirconium, aluminium, lanthanum, andstrontium is used. Herein, the silicate compound is defined as acompound having a structure in which the oxide of the metal is containedin the dioxide of silicon (SiO₂). Further, the dielectric constant ofthe gate insulating film is preferably up to about 300. The reason forthis is as follows: if it exceeds 300, the film thickness of the gateinsulating film becomes too large.

When the gate insulating film is made of a plurality of layers, it ispossible to adopt a laminated structure in which a layer comprising theoxide of at least one metal selected from the group consisting oftitanium, tantalum, hafnium, zirconium, aluminium, lanthanum, andstrontium, and under this layer, a layer comprising the silicatecompound of the metal are provided.

It is preferable that the source region and the drain region do notcontain the metal contained in the insulating film, or contain the metalin a concentration of 10¹¹ atom/cm² or less. The gate electrode ispreferably a metal selected from at least one selected from the groupconsisting of tungsten, titanium, and molybdenum, or a nitride thereofor a silicide thereof.

Further, in order to attain the second object, a method formanufacturing a semiconductor device according to one aspect of thepresent invention, includes the steps of: forming an insulating filmhaving a higher dielectric constant than that of a silicon dioxide filmon a semiconductor substrate, and forming a conductive film on theinsulating film; processing the conductive film into a gate electrode;removing the insulating film having a higher dielectric constant so thatthe part underlying the gate electrode is left, and the end portions ofthe residual part are positioned inwardly of the end portion on the sideon which a source region is to be formed and the end portion on the sideon which a drain region is to be formed of the gate electrode, andthereby allowing the residual part to serve as a gate insulating film;forming a second insulating film having a lower dielectric constant thanthat of the gate insulating film at least laterally in the gate lengthdirection of the gate electrode, and on the semiconductor substrate; andimplanting a dopant into the substrate through the second insulatingfilm by an ion implantation method to form the source region and thedrain region, and allowing the source region and the drain region toextend into the underlying portion of the gate insulating film.

Still further, in order to attain the second object, a method formanufacturing a semiconductor device according to another aspect of thepresent invention includes the steps of: forming a first insulating filmhaving a higher dielectric constant than that of a silicon dioxide filmon a semiconductor substrate, forming a second insulating film having ahigher dielectric constant than that of the first insulating film on thefirst insulating film, and forming a conductive film on the secondinsulating film; processing the conductive film into a gate electrode;removing the second insulating film so that the part underlying the gateelectrode is left, and the end portions of the residual part arepositioned inwardly of the end portion on the side on which a sourceregion is to be formed and the end portion on the side on which a drainregion is to be formed of the gate electrode, and thereby allowing theresidual part to serve as a gate insulating film; and implanting adopant into the substrate through the first insulating film by an ionimplantation method to form the source region and the drain region, andallowing the source region and the drain region to extend into theunderlying portion of the gate insulating film.

It is preferable that the insulating film having a higher dielectricconstant is formed in amorphous state, and the removal of the insulatingfilm having a higher dielectric constant is partially performed by dryetching, and then further performed by wet etching. Further, it ispreferable that the insulating film having a higher dielectric constantis crystallized after wet etching. Still further, the removal of theinsulating film having a higher dielectric constant is performed suchthat the end portions of the residual part are positioned inwardly fromthe respective end portions on the source region side and on the drainregion side of the gate electrode by 15 nm to 25 nm, respectively. Theresidual part serves as the gate insulating film, and hence each of theend portions thereof has the same meaning as that of each of the endportions of the gate insulating film described above.

The implantation of the dopant can be performed by an oblique ionimplantation method. The materials for the gate insulating film and thematerials for the gate electrode are the same as described above.Further, it is possible that the gate electrode is a polysilicon, and aplurality of the gate electrodes have mutually different work functionsby using different substances for the ion implantation from one gateelectrode to another. The preferred materials and the like of the gateinsulating film and the gate electrode are the same as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D are views showing the manufacturing process of asemiconductor device of Example 1 of the present invention;

FIGS. 2A to 2C are views showing the manufacturing process of thesemiconductor device of Example 1 of the present invention;

FIGS. 3A to 3C are views showing the manufacturing process of asemiconductor device of Example 2 of the present invention;

FIGS. 4A and 4B are views showing the manufacturing process of thesemiconductor device of Example 2 of the present invention;

FIG. 5 is a diagram showing the relationship between the equivalentthickness and the impurity concentration of a gate insulating film inthe channel direction for illustrating the present invention;

FIGS. 6A to 6C are views showing the manufacturing process of asemiconductor device of Example 3 of the present invention; and

FIGS. 7A to 7C are views showing the manufacturing process of thesemiconductor device of Example 3 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1

Below, an example of the present invention will be described byreference to FIGS. 1A to 1D, and FIGS. 2A to 2C. In a silicon substrate101 in which a desired impurity profile of a P-, and N-well structure,or the like has been previously formed, a channel-embedded type elementisolation region structure 102 is formed by a known technology.Thereafter, the silicon substrate surface is washed, and further, anoxide film on the silicon substrate surface is removed. Subsequently, atitanium oxide 103 which is a high dielectric constant insulating filmhaving a higher dielectric constant than that of a silicon dioxide film,a metal film serving as a gate electrode 104, and a silicon dioxide film105 which serves as a mask for gate processing are successively formed,resulting in the structure shown in FIG. 1A. The titanium oxide has beenformed by a CVD process. At this process, it has been deposited inamorphous state by controlling the formation temperature and the like.Further, as the metal film serving as the gate electrode, there has beenused a film formed by depositing a tungsten film with a sputteringmethod.

Then, the silicon dioxide film 105 and the tungsten film are processedby using conventional lithography and dry etching technologies to formthe gate electrode 104. At this step, a part of the titanium oxide film103 has been also etched due to the characteristics of dry etching. Inconsequence, the top thereof has been etched inwardly from the endportions in the gate length direction of the gate electrode 104 toobtain the structure of FIG. 1B. At this step, it is so configured thatthe end portions of the top of the titanium oxide film 103 arepositioned inwardly from the respective end portions of the gateelectrode 104 by about 15 to 25 nm, respectively. In other words, thegate insulating film exhibits a large action at the thickest sitethereof, so that the end portions of this site may be placed at theposition described above.

It is also acceptable that dry etching is performed by changing thepreviously used etching gas into a gas for etching the titanium oxide.However, it is more preferable that the titanium oxide film 103 isremoved by wet etching in order to prevent damage to the substrate. Inthis step, the titanium oxide film 103 has been etched with a mixedsolution of hydrofluoric acid, nitric acid, and acetic acid, resultingin the structure shown in FIG. 1C. Incidentally, our study proves asfollows. Namely, when the metal oxide film has been crystallized, thewet etching rate becomes extremely low. Therefore, the film is formed inamorphous state at the time of film deposition as described above. Then,after the formation of the structure of FIG. 1C, the deposited film iscrystallized by a heat treatment. This process is easier from theviewpoint of the process. Subsequently, a thin silicon dioxide film 106has been formed by a CVD process (FIG. 1D).

Further, a source/drain region 107 is formed by an ion implantationmethod and annealing. In this step, it is essential in improving thedevice characteristics that the boundary between the source/drain region107 and the channel region underlies the region in which the titaniumoxide film 103 which is a high dielectric constant insulating filmexists (FIG. 2A).

Further, an interlayer insulating film 108 ensuring a relatively highdry etching rate has been deposited by a plasma CVD process, and thenthe contact region has been patterned with a photoresist 109 by using alithography process (FIG. 2B). A contact is formed by using thephotoresist 109. By using a difference in etching rate between theinterlayer insulating film 108 and the silicon dioxide film 106, it ispossible to form a contact hole on the source/drain region 107 in aself-aligned manner.

Further, a metal film 110 serving as a wiring layer has been depositedthereon (FIG. 2C), and patterned to form a MISFET structure. Thecharacteristics of the MISFET of this structure have been evaluated. Asa result, it has been shown that the MISFET has good devicecharacteristics. Further, it has been also shown that the concentrationof the metal constituting the high dielectric constant insulating filmcontained in the source/drain region 107, i.e., titanium is 10¹¹atom/cm² or less.

Incidentally, in this example, a titanium oxide is used as the highdielectric constant insulating film. However, even when the oxide or theoxynitride of at least one metal selected from the group consisting oftitanium, tantalum, hafnium, zirconium, aluminium, lanthanum, andstrontium is used, it is possible to obtain the same effect. Further,even when a silicate compound obtained from CVD using the organic metalcompound of the aforesaid metal (a plurality of metals are alsoacceptable), an organic Si compound, and oxygen as a source gas is used,it is possible to obtain the same effect. The silicate compoundcomprises titanium-Si-oxygen when titanium has been used as the metal.

Further, tungsten is used as the gate electrode. However, even whentitanium, molybdenum, or a nitride thereof or a silicide thereof isused, it is possible to obtain the same effect.

With this semiconductor device, if the insulating film having a highdielectric constant is present on the region in which the channel regionand the source and drain regions continuous with the channel regionoverlap with the gate electrode, it is possible to increase the amountof induced charge flowing through the channel region. On the other hand,a high electric field occurs between the gate edges and the source andthe drain. Therefore, such a configuration has been adopted that aninsulating film having a relatively low dielectric constant such as asilicon dioxide film is disposed at this site. This configuration iseffective for reducing the fringe capacitance.

EXAMPLE 2

Next, a second example of the present invention will be described byreference to FIGS. 3A to 3D, and FIGS. 4A and 4B. In a silicon substrate201 in which a desired impurity profile has been previously formed, achannel-embedded type element isolation region structure 202 is formedin the same manner as in Example 1. Thereafter, the silicon substratesurface is washed, and further, an oxide film on the silicon substratesurface is removed. Subsequently, a high dielectric constant insulatingfilm having a higher dielectric constant than that of a silicon dioxidefilm is formed. Herein, the high dielectric constant insulating film hasbeen formed by a plasma CVD process. At this process, zirconium oxidehas been used as the high dielectric constant material. The insulatingfilm formed in this case is so configured that a so-called silicate film203 comprising zirconium-silicon-oxygen having a relatively lowdielectric constant (to about 10) is formed on the substrate, and azirconium oxide 204 is formed thereon. In consequence, it becomes aninsulating film of a laminated structure. A tungsten film serving as agate electrode 205, and a silicon dioxide film 206 serving as a mask forgate processing have been successively formed thereon, resulting in thestructure shown in FIG. 3A.

Thereafter, the silicon dioxide film 206 and the tungsten film areprocessed by using conventional lithography and dry etching technologiesto form the gate electrode 205. Further, dry etching is performed bychanging the previously used etching gas into a gas for etching thezirconium oxide 204. In consequence, the silicate film 203 isselectively left to obtain the structure of FIG. 3B. Herein, thesilicate film 203 is roughly identical in physical properties with thesilicon dioxide. Accordingly, it is possible to increase the differencein etching rate with the zirconium oxide film for dry etching, which isadvantageous for obtaining the structure of FIG. 3B. Further, thezirconium oxide 204 has been so configured that each end portionsthereof are positioned inwardly from the respective end portions in thegate length direction of the gate electrode by about 15 to 25 nm,respectively.

Subsequently, source/drain region 207 is formed by an ion implantationmethod and annealing. In this step, it is essential in improving thedevice characteristics that the boundary between the source/drain region207 and the channel region is allowed to underlie the region in whichthe zirconium oxide film 204 exists by controlling the ion implantationconditions and the annealing conditions (FIG. 3C).

Incidentally, the concentration of zirconium in the silicate film 203 isseveral percent, and the amount of zirconium atoms knocked on into thesubstrate is about 10¹¹ atom/cm². Thus, it is possible to reduce theamount down to 10% or less of the amount in the case of the ionimplantation through a zirconium oxide film. Therefore, in this step,intentionally, the through film for ion implantation used in Example 1is not used.

Further, an interlayer insulating film 208 ensuring a relatively highdry etching rate has been deposited by a plasma CVD process, and thenthe contact region has been patterned with a photoresist 209 by using alithography process (FIG. 4A). A contact has been formed by using thephotoresist 209 as a mask, and a metal film 210 serving as a wiringlayer has been deposited thereon (FIG. 4B), and patterned to form aMISFET structure.

Herein, FIG. 5 shows the relationship between the equivalent thickness(the insulating film thickness in terms of the dielectric constant ofthe silicon dioxide film) and the impurity concentration of the gateinsulating film in the channel direction. Thus, it is possible tosufficiently perform the induction of charge, and increase the channelcurrent due to the fact that the site with a small equivalent thicknessoverlies the source/drain region connected to the channel region. On theother hand, by increasing the equivalent thickness on a region otherthan the aforesaid region, it is possible to resultantly improve theoperation speed of the device without increasing the fringe capacitance.

The characteristics of the MISFET of this structure have been evaluated.As a result, it has been shown that the MISFET has good devicecharacteristics.

Incidentally, in this example, zirconium oxide is used as the highdielectric constant insulating film. However, even when the oxide or theoxynitride of at least one metal selected from the group consisting oftitanium, tantalum, hafnium, zirconium, aluminium, lanthanum, andstrontium is used, it is possible to obtain the same effect.

Further, for the gate electrode, tungsten is used. However, even whentitanium, molybdenum, or a nitride or silicide thereof is used, it ispossible to obtain the same effect.

EXAMPLE 3

Further, a third example of the present invention will be described byreference to FIGS. 6A to 6C, and FIGS. 7A to 7C. In this example, aplurality of MISFETs are formed, and both of P-type channel and N-typechannel MISFETs are formed. Therefore, a polysilicon is used for thegate electrode material. A P-, or B-doped polysilicon is used as a gateelectrode according to a MISFET, so that the work function varies fromone gate electrode to another.

In a silicon substrate 301 in which a desired impurity profile has beenpreviously formed, a channel-embedded type element isolation regionstructure 302 is formed in the same manner as in Example 1. Thereafter,the silicon substrate surface is washed, and further, an oxide film onthe silicon substrate surface is removed. Subsequently, a highdielectric constant insulating film having a higher dielectric constantthan that of a silicon dioxide film is formed. Herein, the highdielectric constant insulating film has been formed by a plasma CVDprocess. At this process, a zirconium oxide has been used as the highdielectric constant material. The insulating film formed in this case isso configured that a so-called silicate film 303 comprisingzirconium-silicon-oxygen having a relatively low dielectric constant (toabout 10) is formed on the substrate, and a zirconium oxide 304 isformed thereon. In consequence, it becomes an insulating film of alaminated structure. A polysilicon film serving as a gate electrode 305is formed thereon as described above, and P or B is introduced thereintoby the ion implantation method. An appropriate annealing is performed,and then, a silicon dioxide film 306 serving as a mask for gateprocessing is successively formed, resulting in the structure shown inFIG. 6A.

Thereafter, the silicon dioxide film 306 and the P-, or B-dopedpolysilicon film are processed by using conventional lithography and dryetching technologies to form the gate electrode 305. Further, dryetching is performed by changing the previously used etching gas into agas for etching the zirconium oxide 304. In consequence, the silicatefilm 303 is selectively left to obtain the same structure as that ofFIG. 3B shown in the second example. Subsequently, by using a wetetching technology with a hydrofluoric acid, the silicate film 303 isremoved so that the portion of the silicate film 303 underlying the gateelectrode is partly left, resulting in the structure of FIG. 6B. Herein,the silicate film 303 has been so configured that the end portionsthereof are positioned inwardly from the respective end portions in thegate length direction of the gate electrode 305 by about 15 to 25 nm,respectively.

Thereafter, a silicon dioxide film 307 is formed as a through film forion implantation by the CVD method. The profile is shown in FIG. 6C.Herein, the diffusion layer serving as source/drain is made shallow inorder to improve the short channel characteristics. To that end, theimplantation energy for ion implantation is also set at a small value,i.e., 2 KeV. For that reason, the thickness of the through film is alsoset ata small value, i.e., 5 nm. Therefore, as shown in FIG. 6C, thegate electrode side is so configured as to have a depression of about 10to 20 nm in the underlying portion of the gate electrode even after theformation of the through film.

Herein, in order to form a shallow diffusion layer, and cause overlapbetween the source/drain region and the region having a very smallequivalent thickness, an oblique ion implantation technique is used inthis example. In this step, by setting the implantation angle at 30degrees, the source/drain region is allowed to reach the region with asmall equivalent thickness underlying the gate.

The source/drain region has been formed as shown in FIG. 7A by theoblique ion implantation method and annealing. In order toadvantageously cause overlap between the source/drain region and thesite of the gate insulating film, having a very small equivalentthickness in this manner, the control of the depression in the gatesidewall portion described above is also an effective means. Further, ithas been shown that the concentration of the metal constituting the highdielectric constant insulating film, i.e., zirconium contained in thesource/drain region is 10¹¹ atom/cm² or less.

Further, an interlayer insulating film 308 ensuring a relatively highdry etching rate has been deposited by a plasma CVD process, and thenthe contact region has been patterned with a photoresist 309 by using alithography process (FIG. 7B). A contact has been formed by using thephotoresist 309 as a mask, and a metal film 310 serving as a wiringlayer has been deposited thereon (FIG. 7C) and patterned to form aMISFET structure. Incidentally, in this step, a contact hole is formedin a self-aligned manner by using a difference in dry etching ratebetween the interlayer insulating film 308 and the silicon dioxide film307 which is a through film in the same manner as in the first example.

The characteristics of the MISFET of this structure have been evaluated.As a result, it has been shown that the MISFET has good devicecharacteristics, i.e., it is excellent in short channel characteristics,and driving current.

Incidentally, in this example, a zirconium oxide is used as the highdielectric constant insulating film. However, even when the oxide or theoxynitride of at least one metal selected from the group consisting oftitanium, tantalum, hafnium, zirconium, aluminium, lanthanum, andstrontium is used, it is possible to obtain the same effect.

Further, for the gate electrode, tungsten is used. However, even whentitanium, molybdenum, or a nitride or silicide thereof is used, it ispossible to obtain the same effect.

According to the present invention, it is possible to increase the speedof a MISFET device. Further, it is possible to avoid the contaminationof a silicon substrate due to the incorporation of a metallic elementthereinto, and an increase in fringe capacitance.

What is claimed is:
 1. A semiconductor device having a field effecttransistor, said field effect transistor comprising a semiconductorsubstrate, source and drain regions formed in said semiconductorsubstrate, a gate insulating film on said semiconductor substrate, and agate electrode disposed via said gate insulating film on saidsemiconductor substrate, said gate insulating film being an insulatingfilm having a higher dielectric constant than that of a silicon dioxidefilm, the upper end portions in the gate length direction of said gateinsulating film being positioned inwardly from the respective endportions of the gate electrode and inwardly from respective lower endportions of said gate insulating film, on the source side and on thedrain side of said gate electrode, and said upper end portions of saidgate insulating film being positioned in a region in which said gateelectrode overlaps with a the source region and athe drain region inplan configuration.
 2. The semiconductor device according to claim 1,wherein an insulating film having a lower dielectric constant than thatof said gate insulating film is provided laterally of the end portionsin the gate length direction of said gate insulating film, and on saidsemiconductor substrate.
 3. The semiconductor device according to claim1, wherein the upper end portions of the gate insulating film in thegate length direction of said gate insulating film are positionedinwardly from the respective end portions of the gate electrode on thesource side and on the drain side of said gate electrode by 15 nm to 25nm, respectively.
 4. The semiconductor device according to claim 1,wherein said gate insulating film is an oxide, an oxynitride, or asilicate compound of at least one metal selected from the groupconsisting of titanium, tantalum, hafnium, zirconium, aluminum,lanthanum, and strontium.
 5. The semiconductor device according to claim1, wherein said gate insulating film has a laminated structure of alayer comprising an oxide of at least one metal selected from the groupconsisting of titanium, tantalum, hafnium, zirconium, aluminum,lanthanum, and strontium, and a layer comprising a silicate compound ofsaid metal.
 6. The semiconductor device according to claim 1, whereinsaid semiconductor substrate comprises a silicon substrate and whereinsiad source region and said drain region formed in said siliconsubstrate do not contain the metal , or contain metal in a concentrationof 10¹¹ atom/cm² or less.
 7. The semiconductor device according to claim1, wherein said gate electrode is a metal selected from at least oneselected from the group consisting of tungsten, titanium, andmolybdenum, or a nitride thereof or a silicide thereof.
 8. Asemiconductor device according to claim 1, wherein lower end portions ofsaid gate insulating film are formed outwardly of the end portions ofthe gate electrode in said gate length direction.
 9. A semiconductordevice having a field effect transistor, said field effect transistorcomprising a semiconductor substrate, a gate insulating film on saidsemiconductor substrate, and a gate electrode disposed via said gateinsulating film on said semiconductor substrate, said gate insulatingfilm being an insulating film having a higher dielectric constant thanthat of a silicon dioxide film, and the upper end portions in the gatelength direction of said gate insulating film being positioned inwardlyfrom the respective end portions of said gate electrodes and inwardlyfrom respective lower end portions of said gate insulating film on thesource side and on the drain side of said gate electrode, and a sourceregion and a drain region of said field effect transistor extending intothe underlying portion of said gate insulating film.
 10. A semiconductordevice according to claim 9, wherein lower end portions of said gateinsulating film are formed outwardly of the end portions of the gateelectrode in said gate length direction.
 11. A semiconductor devicehaving a field effect transistor, said field effect transistorcomprising a semiconductor substrate, source and drain regions formed insaid semiconductor substrate, a gate insulating film on saidsemiconductor substrate, and a gate electrode disposed via said gateinsulating film on said semiconductor substrate, said gate insulatingfilm being an insulating film having a higher dielectric constant thanthat of a silicon dioxide film, wherein both said gate electrode andsaid gate insulating film overlap the source and drain regions in planconfiguration, wherein said semiconductor substrate is a siliconsubstrate, and wherein said gate insulating film includes metal, furthercomprising means for reducing an amount of metal introduced into saidsilicon substrate from said gate insulating film, said means includingforming upper end portions in a gate length direction of the gateinsulating film inwardly of end portions of the gate electrode andreducing the thickness of the gate insulating film beginning from saidupper end portions of the gate insulating film in areas where said gateelectrode extends over said source and drain regions.
 12. Asemiconductor device according to claim 11, wherein said means forreducing the amount of metal introduced into said silicon substratefurther includes reducing the thickness of the gate insulating film in atapered manner between the upper end portions of the gate insulatingfilm and lower end portions of said gate insulating film.
 13. Asemiconductor device according to claim 12, wherein both said upper endportions and said lower end portions of said gate insulating film areformed in areas where the gate insulating film overlaps the source anddrain regions.
 14. A semiconductor device according to claim 12, whereinsaid lower end portions are formed outwardly of the end portions of thegate electrode in the gate length direction.
 15. A semiconductor deviceaccording to claim 12, wherein the means for reducing the amount ofmetal introduced into the silicon substrate further comprises a secondgate insulating film having a lower dielectric constant than said gateinsulating film formed over areas of said gate insulating filmunderlying said gate electrode between said upper end portions and saidlower end portions of said gate insulating film.
 16. A semiconductordevice according to claim 15, wherein said second insulating film iscomprised of silicon dioxide.
 17. A semiconductor device according toclaim 11, wherein the upper end portions of the gate insulating film inthe gate length direction of said gate insulating film are positionedinwardly from the respective end portions of the gate electrode on thesource side and on the drain side of said gate electrode by 15 nm to 25nm, respectively.
 18. A semiconductor device having a field effecttransistor, said field effect transistor comprising a semiconductorsubstrate, source and drain regions formed in said semiconductorsubstrate, a gate insulating film on said semiconductor substrate, and agate electrode disposed via said gate insulating film on saidsemiconductor substrate. said gate insulating film being an insulatingfilm having a higher dielectric constant than that of a silicon dioxidefilm, wherein both said gate electrode and said gate insulating filmoverlap the source and drain regions in plan configuration, wherein saidsemiconductor substrate is a silicon substrate, and wherein said gateinsulating film includes metal, further comprising means for reducing anamount of metal introduced into said silicon substrate from said gateinsulating film, said means including forming upper end portions of thegate insulating film inwardly in a gate length direction from endportions of the gate electrode, reducing the thickness of the gateinsulating film in areas where the gate electrode extends over thesource and drain regions by reducing the thickness of the gateinsulating film in a tapered manner between the upper end portions ofthe gate insulating film and lower end portions of the gate insulatingfilm, which lower end portions of the gate insulating film extendoutwardly from the respective end portions of the gate electrode in saidgate length direction, wherein both said upper end portions and saidlower end portions of said gate insulating film are formed in areaswhere the gate insulating film overlaps the source and drain regions,and further comprising a second gate insulating film having a lowerdielectric constant than said gate insulating film, the second gateinsulating film being formed over areas of said gate insulating filmunder the gate electrode and between said upper end portions and saidlower end portions of the gate insulating film.
 19. A semiconductordevice according to claim 18, wherein said second insulating film iscomprised of silicon dioxide.
 20. A semiconductor device according toclaim 18, wherein the upper end portions of the gate insulating film inthe gate length direction of said gate insulating film are positionedinwardly from the respective end portions of the gate electrode on thesource side and on the drain side of said gate electrode by 15 nm to 25nm, respectively.
 21. A semiconductor device having a field effecttransistor, said field effect transistor comprising a semiconductorsubstrate, source and drain regions formed in said semiconductorsubstrate, a gate insulating film on said semiconductor substrate, and agate electrode disposed via said gate insulating film on saidsemiconductor substrate, said gate insulating film being an insulatingfilm having a higher dielectric constant than that of a silicon dioxidefilm, wherein said gate electrode and said insulating film overlap saidsource and drain regions in plan configuration, and further comprisingmeans for reducing fringe capacitance in said areas where said gateelectrode overlaps said source and drain regions, said means includingforming said gate insulating film so that upper end portions in the gatelength direction of the gate insulating film are position inwardly ofend portions of said gate electrode and inwardly of lower end portionsof said gate insulating film and said upper end portions of said gateinsulating film are formed in a region in which the gate electrodeoverlap the source and drain regions in plan configuration.
 22. Asemiconductor device according to claim 21, wherein said lower endportions in the gate length direction of said gate insulating film areformed outwardly of said end portions of said gate electrode and whereinsaid means for reducing fringe capacitance further comprises forming asecond gate insulating film having a lower dielectric constant than saidgate insulating film in an area covering the gate insulating film underthe gate electrodes and between the upper end portions and lower endportions of the gate insulating film.
 23. A semiconductor deviceaccording to claim 21, wherein the upper end portions of the gateinsulating film in the gate length direction of said gate insulatingfilm are positioned inwardly from the respective end portions of thegate electrode on the source side and on the drain side of said gateelectrode by 15 nm to 25 nm, respectively.